Wednesday, March 9, 2011

more explosions!

Update (March 20, 2011): Davin was interviewed by the RSC's Chemistry World. Go check it out!

You may recall a post from last November on a JACS paper on the explosive nature of nitrotetrazolate-2N-oxides. The paper also got some attention from the inimitable Derek Lowe in his popular series, "Things I Won't Work With."

Well, the Klapoetke group has gone one step further and published another paper in Inorganic Chemistry (subscription required) on crazy insane explosives, with probably the best TOC graphic of all time (of all time!):

That structure has a chain of 10 nitrogen atoms. That's right. 10.

Rather than try to explain the science behind this paper on my own, I emailed one of the co-authors, Davin Piercey for assistance. Davin did his undergrad research in our lab, and was happy to get back to me right away with an explanation (and a video!).

DGP: So within 24 h of the 1,1’-azobis(tetrazole) paper being online, there is already interest in this due to a combination of interesting properties and the scientific novelty arising from a chain of ten connected nitrogen atoms. Joel and I go way back so I agreed to write a guest post on this subject.

Describe the science behind this paper, and what makes this compound so explosive?

DGP: Generally explosive behavior results from one of two general sources, molecules containing fuel and oxidizer in the same molecule, or high heat of formation materials. Of course, both sources can be at play within one molecule. 1,1’-azobis(tetrazole) is an example of the latter type of material, where the high heat of formation results from mostly high nitrogen content, with minor contribution by strained bonds in the five-membered tetrazole rings. The reason high nitrogen content leads to explosive behavior, is the low thermodynamic stability of N-N bonds relative to the triple bond in nitrogen gas; explosives are metastable when compared to their detonation products (generalized: N2, CO2, CO, H2O).
The more N-N bonds present, the higher the higher the heat of formation and the lower the stability of the compound, where stability is manifested by both thermal and mechanical sensitivities.

As mentioned in the paper, 1,1’-azobis(tetrazole) has a heat of formation near that of 1,4-diazido-2,3,4,5-tetrazene, another exceedingly sensitive, high heat of formation material.

Eight-nitrogen chains were well known at the time, so preparing a longer chain was the academic motivation of this work.

What’s the craziest thing that’s happened to you in working with this stuff? How do you deal with it safely?

DGP: Safety is of course paramount when dealing with explosive materials, and the easiest way to be safe is to work on small scale. I was only working with 170 mg of precursor giving a maximum product yield slightly below this mass. However even 100 mg of quality explosive can punch a clean hole through 1mm aluminum so the next major factor is standoff: flasks containing explosives never get held in the palm of one’s Kevlar-covered hand, but rather are either held with a clamp, or by the neck a finger’s length away. With these two precautions taken, the remainder is personal protection equipment for potential shrapnel; Kevlar gloves and arm protectors work wonders, and basic body armour or leather, face shield, and hearing protection takes care of the rest. Another hidden danger with sensitive explosives is static discharge, so the experimenter is always electrically grounded.

Finally, for exceedingly sensitive materials such as this, keeping the material wet greatly reduces sensitivity, 1,1’-azobis(tetrazole) could not be repeatedly manipulated dry without exploding.

The craziest thing that happened while working with this stuff was once a raman tube was loaded with dry material, as it slid down the tube to the bottom it chose to explode. What was annoying was the filtercake of remaining material placed approximately 80 cm from the explosion must have got hit by the shrapnel, as it exploded concurrently; I was annoyed, I had grown tired of making it repeatedly. I switched to only handling it wet after that and no more incidents occurred.

Also amusing was the explosion while rotovapping an acetonitrile solution of it, it had been done several times before without incident, but this time I chose to slow it as it precipitated to watch. When the rotovap was slowed the flask exploded. The flask it was in is shown next to an intact flask on the paper’s table of contents image.

Due to proper protective measures, these explosions were only an inconvenience.

What drew you to study these explosive materials?

DGP: Their inherent awesomeness… well, that and pushing the limits of what can exist, and trying to stabilize compounds on the limits of existence.

Do you have any battlescars?

DGP: Nope… or at least not yet. :P ;)

Davin was also very gracious in sending along a video he recorded showing the explosion that generated one of the fractures in the above TOC graphic:


Will said...

Saw this pop up, and have been meaning to read through it for a bit now. Meanwhile was just ogling the awesome TOC image in my reader.

Wow, infiniflux is really stepping up, giving interviews now. In the big time.

Ψ*Ψ said...

Nice video/interview! I don't think I'll ever have the balls to do that kind of science.
(I also wish Klapötke would put a video in the SI of every paper he put out, just for sheer awesomeness...most of us don't get to see things blow up too often.)

Chemjobber said...

Wow! Every chemist wishes they could do that!

explosci said...

MOAR video ;)